1. Field of the Invention
The present invention generally relates to a positioning apparatus and a positioning information receiving method/apparatus used in the GPS system. More specifically, the present invention is directed to such portable type positioning apparatus and positioning information receiving method/apparatus, capable of minimizing a shift between reception timing and transmission timing of GPS positioning information when GPS positioning operation is restarted.
2. Description of the Related Art
Conventionally, in positioning apparatuses used to measure present positions of the own positioning apparatuses in the GPS (global positioning system) system, the present own positions can be measured by receiving the navigation signals (namely, positioning information) known as ephemeris and almanac signals transmitted from a plurality of GPS satellites. It should be noted that the ephemeris signal corresponds to data related to orbit information of the own satellite as a GPS signal transmitting source and timepiece correction information, whereas the almanac signal corresponds to data related to brief orbit information about all of the GPS satellite. To receive data transmitted from the respective positioning satellites, reception timing of this data is required to be synchronized with transmission timing of the data transmitted from the respective GPS satellites during reception operation. In other words, these positioning apparatuses must capture the GPS satellites. However, since the GPS satellites and these positioning apparatuses are always moved, this transmission timing is continuously changed. In connection with such a positional change, for instance, since a present position of a car navigation apparatus with employment of the GPS system is updated every second, this car navigation apparatus may synchronize the reception timing to the transmission timing to some allowable extent. That is, such a GPS type car navigation apparatus continuously may establish the synchronization between the reception timing and the transmission timing up to a maximum car speed, e.g., several hundreds Km/h. Namely, while the reception timing is once synchronized with the transmission timing, the maximum shift between the transmission timing and the reception timing, which is caused by movement of both the car navigation apparatus and the relevant GPS satellites, is corrected during the next position measuring process operation. In other words, the present position measuring operation is once commenced, and then this present position measuring operation is continuously carried out in such a car navigation apparatus.
However, for example, when a wrist watch type portable positioning apparatus is realized, this portable positioning apparatus may be readily adversely influenced by geographical features and disturbance objects, so that such positioning information can be hardly received, as compared with such a car navigation apparatus capable of updating the present position every second, namely capable of capturing the GPS satellites every second. Furthermore, since the most portable type positioning apparatuses employ cells as power sources thereof, operators are required to frequently turn OFF these power sources. As a result, in such a portable positioning apparatus, every time the present position is measured, the reception timing must be synchronized with the transmission timing of the navigation signal so as to receive the navigation signal, or to capture this GPS satellites. Therefore, there is a problem that lengthy time is necessarily required so as to measure the present position of the own portable positioning apparatus. Also, since relatively high electric power is required in order to measure the present own position, there is another problem that the lifetime of the battery mounted on the portable positioning apparatus is shortened.